Embedded Fe Nanoparticles Research Articles

FePt: LaSrFeO4 nanocomposite film prepared by magnetron and pulsed laser co-deposition method

The extensive application of a multifunctional composite film of metal nanoparticles embedded in a dielectric matrix is remarkable. Due to the oxidation susceptibility of atomic iron, it is difficult to directly fabricate embedded Fe nanoparticles in an oxide dielectric matrix with a Fe target. Because La0.5Sr0.5FeO3 can be decomposed into LaSrFeO4 and α-Fe, ferromagnetic and optical absorption FePt:LaSrFeO4 composite films were successfully fabricated at room temperature using Pt and La0.5Sr0.5FeO3 as targets via magnetron and pulsed laser co-deposition. Further annealing was performed on the FePt:LaSrFeO4 composite films. FePt is chemically disordered face-centered cubic phase (A1 structure) below 600 oC annealing and chemically ordered face-centered tetragonal phase (L10 structure) above 600 oC annealing. With increasing the annealing temperature, a redshift of the absorption peak from 256 to 285 nm is seen, which can be attributed to the size growth of the LaSrFeO4 and FePt nanoparticles in the composite films. The strongest absorption peak at around 269 nm for the 600 oC annealed sample can be attributed to the high crystallographic quality and relatively tiny grain size of FePt particles with uniform distribution. FePt:LaSrFeO4 composite films are ferromagnetic and optically absorbent, making them suited for multifunctional applications. Furthermore, magnetron and pulsed laser co-deposition techniques have the potential to produce multiferroic oxides, in which the coupling of different ordering processes e. g. ferroelectricity and ferromagnetism provides the potential for a new breed of multifunctional devices.

Magnetic and structural changes in Cu1−xAlx alloy matrix – Embedded Fe nanoparticle systems

Abstract We describe the atomic structure and magnetism in Fe nanoparticles (∼2 nm) ebedded in a Cu1−xAlx alloy matrix. Nanocomposite films for these studies were prepared directly from gas phase using a flexible co-deposition technique under Ultra-High Vacuum (UHV) conditions. Fe nanoparticles and the alloy matrix were prepared using a gas aggregation source and MBE sources respectively. Extended x-ray absorption fine structure (EXAFS) experiments indicate that the embedded Fe nanoparticles retain a bcc structure for Al-contents greater than x = 0.13 but, for Al-contents lower than this value, Fe nanoparticles have both fcc and bcc structures. The magnetic moment per Fe atom initially increases with increasing Al-content due to the bcc structure becoming more dominant in the embedded nanoparticles as the Al-content is increased, but then decreases with further increase in Al-content. This decrease is consistent with a modest degree of alloying between Fe and Al atoms at the particle/matrix interfaces.

Bioinspired Single-Walled Carbon Nanotubes as a Spider Silk Structure for Ultrahigh Mechanical Property.

Due to its unique hierarchical structure, natural spider silk features exceptional mechanical properties such as high tensile strength and great extensibility, making it one of the toughest materials. Herein, we design bioinspired spider silk single-walled carbon nanotubes (BISS-SWCNTs) that combine the hierarchical structure of spider silk and the high strength and conductivity of SWCNTs. To imitate the hierarchical structure, Fe nanoparticles are embedded on the surface of directly synthesized SWCNTs skeleton followed by coating an amorphous carbon layer. The carbon layer forms the spider silk-featured skin-core structure with SWCNTs, thus making the tube junction tougher. The embedded Fe nanoparticles act as glue spots for preventing interfacial slippages between the BISS-SWCNTs and the reinforced matrix. With only 2.1 wt % BISS-SWCNTs added, the tensile strength and Young's modulus of the BISS-SWCNTs/PMMA composites can be improved by 300%. More importantly, the BISS-SWCNTs also retain the high conductivity and transmittance of the pristine SWCNTs film. This unique bioinspired material will be of great importance in applications of multifunctional composite materials and has important implications for the future of biomimetic materials.

Tailored Fe3C-derived carbons with embedded Fe nanoparticles for ammonia adsorption

Carbide-derived carbons are synthesized by chlorination of Fe3C at temperatures ranging from 200 to 1000 °C. The complex extraction method of Fe from Fe3C at moderate temperatures (600 °C) allows for the tailored inclusion of FeCl2, FeCl3, or Fe nanoparticles in the resulting CDC by controlling the synthesis conditions and post-treatment methods. In this study, we extend the synthesis to other temperatures in order to understand the role of chlorination temperature on the physical and textural properties of the resulting CDC. We also examine the activity of Fe3C-CDCs with embedded FeCl3 nanoparticles for ammonia adsorption. Materials synthesized at 600 °C show exceptional results in ammonia breakthrough experiments, and achieved dynamic loadings of 1.88 mmol g−1 at 0% relative humidity and 3.44 mmol g−1 at 75% relative humidity calculated at initial breakthrough when [NH3] > 0 ppm. NH3 temperature programmed desorption (NH3-TPD) and Fourier Transform Infrared Spectroscopy (FTIR) experiments suggest that the uptake is primarily due to ammonia complexation with FeCl3 nanoparticles under dry conditions, and additional interactions with trapped chlorine in the presence of water.

MIL-100 derived nitrogen-embodied carbon shells embedded with iron nanoparticles.

The use of metal-organic frameworks (MOFs) as templates and precursors to synthesize new carbon materials with controllable morphology and pre-selected heteroatom doping holds promise for applications as efficient non-precious metal catalysts. Here, we report a facile pyrolysis pathway to convert MIL-100 into nitrogen-doped carbon shells encapsulating Fe nanoparticles in a comparative study involving multiple selected nitrogen sources. The hierarchical porous architecture, embedded Fe nanoparticles, and nitrogen decoration endow this composite with a superior oxygen reduction activity. Furthermore, the excellent durability and high methanol tolerance even outperform the commercial Pt-C catalyst.

Embedded Fe Nanoparticles in the MgO Layer of CoFeB/MgO/CoFeB Perpendicular Magnetic Tunnel Junctions

In this paper, we report the electric and magnetic effects after inserting Fe nanoparticles into the MgO layer of a Ta(25)/Co <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">20</sub> Fe <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">60</sub> B <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">20</sub> (1.3)/MgO(1)/Fe(x)/MgO(1)/Co <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">40</sub> Fe <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">40</sub> B <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">20</sub> (2.2)/Ta(5) structure. The samples were annealed at 300 °C without external magnetic field. Temperature dependence of resistivity and the anomalous Hall effect were used to infer the morphology of the Fe layer. With the addition of Fe nanoparticles, the optimal tunnel magnetoresistance ratio can be increased by up to 111.2%.

Synthesis of embedded iron nanoparticles in Fe3C-derived carbons

Carbide-derived carbons with embedded Fe nanoparticles are synthesized by partial chlorination of iron carbide at 600°C. Interestingly, the residual Fe studied by X-ray absorption near edge spectroscopy, scanning electron microscopy, and transmission electron microscopy show the extraction process does not follow a layer-by-layer extraction process, as proposed in the literature for the chlorination of other carbides. Instead, a large percentage of iron carbide converts to iron (II) and iron (III) chloride nanoparticles, which remain trapped within the resulting nanoporous carbon framework. Further reductive treatment can be used to produce dispersed Fe nanoparticles with an average particle diameter approaching 10nm.

Effect of large mechanical stress on the magnetic properties of embedded Fe nanoparticles.

Magnetic nanoparticles are promising candidates for next generation high density magnetic data storage devices. Data storage requires precise control of the magnetic properties of materials, in which the magnetic anisotropy plays a dominant role. Since the total magneto-crystalline anisotropy energy scales with the particle volume, the storage density in media composed of individual nanoparticles is limited by the onset of superparamagnetism. One solution to overcome this limitation is the use of materials with extremely large magneto-crystalline anisotropy. In this article, we follow an alternative approach by using magneto-elastic interactions to tailor the total effective magnetic anisotropy of the nanoparticles. By applying large biaxial stress to nanoparticles embedded in a non-magnetic film, it is demonstrated that a significant modification of the magnetic properties can be achieved. The stress is applied to the nanoparticles through expansion of the substrate during hydrogen loading. Experimental evidence for stress induced magnetic effects is presented based on temperature-dependent magnetization curves of superparamagnetic Fe particles. The results show the potential of the approach for adjusting the magnetic properties of nanoparticles, which is essential for application in future data storage media.

Ferromagnetism of Dy films containing embedded Fe atoms and nanoparticles

We have studied the magnetic behaviour of polycrystalline dysprosium films grown in their pure state and containing Fe impurity. The films were grown by MBE in ultra-high vacuum and Fe impurity was introduced either as Fe atoms from a conventional MBE source or as 1.8 nm diameter Fe nanoparticles from a gas aggregation source. We show that with a suitable magnetothermal history it is possible to produce a large thermal hysteresis up to room temperature in all samples. In the Dy ferromagnetic state both types of Fe impurity cause a reduction in the observed magnetisation but the reduction of average moment observed in the case of the Fe nanoparticles is much greater than that for atoms for a similar quantity of Fe. Despite the low solubility of Fe in Dy EXAFS data clearly indicates alloying in the case of embedded Fe nanoparticles. We attribute the low moment in the Dy films containing nanoparticles to alloying within the particles producing a significant proportion of high-Fe-concentration Dy–Fe alloy.

Supported and embedded Fe nanoparticles: Influence of the environment on shape and interface contributions to the magnetic anisotropy

A continuously working arc cluster ion source was used to prepare mass-filtered Fe nanoparticles with a mean size of 6 to 10 nm. Their structure was determined by HRTEM. The nanoparticles were deposited into an Al matrix and additionally on a W(110) substrate for comparison. Within the matrix they maintain their spherical shape and do not show any magnetic anisotropic effect. For uncapped Fe nanoparticles on a tungsten surface, a flattening is observed by STM and the nanoparticles exhibit a distinct magnetic anisotropy with the easy magnetization axis being in the surface plane. Correlating both investigations we conclude that this observation is due to shape and interface-induced contributions to the magnetic anisotropy.

Ion beam synthesis of Fe nanoparticles in MgO and yttria-stabilized zirconia

To form embedded Fe nanoparticles, MgO(001) and YSZ(001) single crystals have been implanted at elevated temperatures with Fe ions at energies of 100keV and 110keV, respectively. The ion fluence was fixed at 6×1016cm−2. As a result, γ- and α-phase Fe nanoparticles were synthesized inside MgO and YSZ, respectively. A synthesis efficiency of 100% has been achieved for implantation at 1273K into YSZ. The ferromagnetic behavior of the α-Fe nanoparticles is reflected by a magnetic hyperfine field of 330kOe and a hysteretic magnetization reversal. Electron holography showed a fringing magnetic field around some, but not all of the particles.

Magneto-optical response of isolated and embedded Fe nanoparticles

The magneto-optical response of nanometric Fe particles with varying size and shape has been studied, both in sputtered single layers and pulsed laser deposited nanocomposite films. The shape of Fe nanoparticles was controlled by varying growth conditions. An effective medium theory for arbitrary particle shapes has been derived and used to simulate the experimentally measured magneto-optical transverse Kerr spectra. The simulations show that the transverse Kerr magneto-optical spectra depend on the particles shape and correlate well with the experimentally determined spectra. From this result, it is deduced that Fe nanoparticles with dimensions down to 3-4 nm keep their bulk magneto-optical constants. On the other hand, large magneto-optical signals are reported in multilayered structures due to interferential effects.